In general, when a power module is mounted on a printed circuit board, a lead terminal of the power module is inserted into a through hole formed in the printed circuit board, and is soldered to electrically connect the power module to the printed circuit board. However, since a large electric current flows through a terminal of, for example, a power supply in a large-capacity power module, a terminal for screwing which has a large area of contact with the printed circuit board is used instead of soldering the lead terminal. Further, even in a large-capacity power module, a lead terminal is used for a terminal of a signal wire or the like in which a small electric current flows. Accordingly, a lead terminal for soldering and a terminal for screwing are both disposed on one power module.
In mounting such a power module on the printed circuit board, when a terminal for screwing (to be referred to as a screw terminal hereinafter) is screwed after the lead terminal is soldered, a crack or the like may occur due to stress generated upon screwing and applied to the solder connection area of the lead terminal, thus lowering the connection reliability. Further, when the lead terminal is soldered after the screw terminal is screwed, the tightening force of the screw is decreased due to heat generated upon soldering, and retightening of the screw is necessary. Accordingly, since a screwing operation after soldering becomes necessary regardless of whether the lead terminal or the screw terminal is first mounted, there is a need to reduce stress acting on the soldering area upon screwing.
For example, Patent Literature 1 discloses a conventional technique for reducing stress acting on the soldering area. In Patent Literature 1, in the printed circuit board having a screw hole for fixing the power module, a slit for reducing the stress is formed around the screw hole.